The present invention is directed to a load-distributive washer for use in attaching compressible material to a base member. One example of such usage is in affixing compressible insulations to roof decks or the like on what is known as a builtup roof.
In formulating the builtup roof, a compressible insulating material is secured to the metallic, wooden or concrete roof deck. This insulation generally has either a paper or foil backing layer secured to one surface. Fasteners such as nails with large washers are used to secure the insulation to the deck followed by applications of asphalt and paper or cloth membranes to form a water tight seal.
As materials are moved about on the roof, a workman may step on or near a washer or cause a wheelbarrow or other equipment to roll over or near a washer. Such localized applications of force can cause the fastener head to pop through the upper membrane or the edge of the washer to pierce the backing layer. Such discontinuities in either the membrane or the backing layer can permit the influx of the asphalt or moisture into the insulation. Such occupation of the interstices of the insulating material reduces the effectiveness of the insulation and can result ultimately in a leaky roof.
Various attempts have been made to correct this problem. One such solution employs a fastener and washer which as a unit can provide some limited movement relative to the insulation and to the metal deck. A principal drawback of such a system is that as the fastener moves relative to the deck, it tends to ream the hole which can result in failure of the fastener. Further, this system is restricted to use with a nail and cannot employ a screw which can provide superior pullout characteristics.
The present invention is directed to a washer which can float relative to the fastener in response to a force directed against or near the load-distributing flange of the washer. An axially extending projection has an internal diameter which exceeds that of the fastener head and a length which is several times the height of the head. The fastener, then, remains securely and immovably fixed to the roof deck while the washer is free to fall and rise responsive to the contraction and expansion of the insulation during and following the application of a compressive force. Such a washer can readily be used with either a nail or screw type mechanical fastener.
For some applications, the washer is preferably made of a resilient plastic material. A plastic washer of this type can further deflect under the application of localized forces preventing the edge of the washer from digging into the backing layer.
An additional feature which this washer can have is a flexible snap ring positioned within the throughbore in the washer. When the fastener is inserted through the washer, the flexible ring will deflect to permit passage of the fastener head and provide a snap fit between the washer and fastener. This will provide an upper limit to the maximum amount of relative movement between the fastener and the washer which is possible. Ordinarily, this upper limit will not be reached since the length of the washer projection will be selected such that under normal load conditions, the compressibility of the insulation will limit further downward movement before the head engages the resilient ring. If the maximum washer deflection is reached, however, the resilient ring will substantially increase the resistance to movement and prevent the fastener head from puncturing the membrane. The resilient ring secondarily reduces the size of the aperture above the fastener head and decreases the likelihood that adhesive or asphalt will fill up the throughbore and reduce the floating capability of the washer.
Other features, characteristics, and advantages of the present invention will become apparent after a reading of the following specification when taken in conjunction with the accompanying drawings.